Hot on the heels of Finland's contest, the Swedish olympiad finals also took place this weekend, and for those who want to try out the problems, we have put up a site where you can participate during any 5 hour period during this week: https://pofinal19-open.kattis.com/.

If you don't have 5 hours to spare you can also look at the problems directly at https://pofinal19.kattis.com/. The last problem is IMO quite neat.

Oh, you're right. That's further back in ICPC history than I've looked. :) I guess it's not too surprising that it has appeared before given the simple graph reformulation, though it does at least require a bit of thinking to reduce it to that.

I had an O(n^3 log n) solution for that problem. I find it not obvious how to improve the solution for the sparse case where |E| is smaller than n^2. I agree that it is a tough problem, it took me several hours to get AC at the Live archive.